This invention relates generally to a computer controller monitoring and control system for a welder and more particularly for a monitoring and control system for calculating the impedance of a welding load connected to a pulsation welder and utilizing this impedance information to determine the internal temperature of the weld and thus determine the quality of the nugget developed during the weld. This is accomplished by generating or absorbing certain counting pulses which are utilized to control the duration of the heat and cool time during the welding cycle.
As is commonly known, a spot weld is created by passing large current pulses, in the case of a pulsation welder, through the two pieces of metal to be welded. This current causes heating at the work-to-work interface, the bulk of the available energy being dissipated at this interface due to the fact that the highest electrical resistance point occurs at the interface. Other points in the electrode-to-electrode assembly may dissipate some energy due to resistance between the electrode and work, and certain other factors. Most conductive materials have a resistivity that depends on the material temperature. Thus, as the temperature increases, the resistivity also increases. Therefore, the resistance of a weld nugget is an indicator of its temperature and the impedance history of a spot weld provides an insight into the distribution of energy dissipated during the creation of that weld. Accordingly, by using selected instrumentation that allows for accurate measurement of the weld impedance, a nondestructive determination of weld quality may be made during the formation of the weld.
The object of the control system is to force the resistance or temperature of the weld to follow a prescribed path throughout the weld. In the system of the present invention, it has been found desirable to make the corrections in the early part of the weld cycle to force the weld up to the melt temperature without causing blowout. In resistance spot welding, the weld nugget is formed in two phases, the first phase being utilized to bring the work up to the melt temperature of the work material and the second phase being utilized to maintain the temperature to permit the nugget to grow. Accordingly, as the impulses during the heat portion of the cycle are sensed, the impedance is calculated and compared to the preselected desired curve and corrections are made to insure that the temperature of the weld, as it is being brought up to the preselected temperature, fits that curve.
The system to be described in presenting the concepts of the present invention include a standard pulsation welder controller presently available on the market. This standard controller typically comprises a system for counting impulses during alternate heat and cool cycles and a circuit for switching the control of the energy from heat to cool in an alternate fashion. The system of the present invention is adapted to be interconnected with the standard pulse welder to sense when a heat portion of the cycle is occurring and when a cool portion of the cycle is occurring. The novel system then determines whether a correction is to be made and whether that correction should be such to apply more or less heat to the work interface. If it is determined that more heat should be applied in a typical situation, the cool cycle will be shortened by generating one or more additional cool cycles within the novel system and feeding these additional cool impulses to the standard welder control to be counted by that standard control. Thus, the standard control is altered to change a pulse generated outside of the standard control to shorten the cool cycle. In the case of lengthening the cool cycle, one or more or the cool pulses is precluded from being counted by the standard control. This could occur by shunting a cool impulse or by maintaining a voltage level at the input circuit at the counter at a particular level such that it appears that an impulse has not been generated when in fact one or more impulses have been generated in a circuit prior to the counter.
The novel system includes a digital computer which is fed data from the welder heads and the computer is utilized to generate output commands to the standard controller. In one embodiment of the invention, voltage sensing leads are interconnected with the welder electrodes to sense the voltage across the work. Also, additional connections are made to accurately sense the current flowing through the work, these measurements being made by standard methods such as standard shunts connected to a portion of the welder load circuit, etc. It is presently contemplated that the voltage will be measured first and then stored for a short period of time until the current is measured. These signals are fed through an analogue to digital converter and control circuit to the computer, the voltage and current data being fed to the computer and control signals being fed from the computer to the converter to control when the voltage and current are sensed. The computer then calculates the impedance of the weld and produces control signals for use by the standard welder controller.
In a typical system, the computer is ordinarily set up to sense a preselected number of load welds, the welds being controlled to produce a desired nugget characteristic. The computer then calculates the impedance for these welds, the number of impulses being in the neighborhood of fourteen for each head being controlled and generates the desired mean curve. The computer then calculates standard deviations for that curve to set up maximum and minimum deviation limits which are acceptable for welds to be performed under the standards set up. The computer then compares future welds with the standards programmed into the computer to determine whether a correction is to be made and whether a correction can be made (the weld is out of limits). The computer also includes a system for updating and weighting additional data being fed during the future welds to permit following of the weld standards to any drift in the welding cycle which may occur as a result of deterioration in the weld electrodes or some other subtle drift in the weld quality.
The system further includes a welder interface circuit for interfacing the computer control signals with the standard welder control. Further, the system includes diagnostic circuits for indicating when a correction is being made and for indicating when a correction cannot be made to mark the work for discard or reworking. The system of the present invention is an improvement on the copending application of Truman Ted Van Sickle and Charles J. Drake, Ser. No. 338,453, filed Mar. 6, 1973, and assigned to the assignee of the instant application.
Accordingly, it is one object of the present invention to provide an improved welder control system.
It is another object of the present invention to provide an improved resistance pulse welding control system.
It is another object of the present invention to provide an improved control system for use in conjunction with a standard impulse welder control system.
It is a further object of the present invention to provide an improved system for calculating the impedance characteristics of a weld as it is being accomplished and comparing the calculated impedance characteristics with the preselected characteristics to determine the progress of the weld.
It is still another object of the present invention to provide an improved impulse welder control system which is capable of comparing weld characteristics with a preselected characteristic standard and applying corrections to the welder to force the weld characteristics to conform to the preselected standard characteristics.
It is still a further object of the present invention to provide an improved impulse welder control which is capable of controlling a multiple number of welder heads and calculating the weld impedance as each impulse of weld current is applied to the work.
It is still a further object of the present invention to provide an improved system such as described in the previous object and apply corrective action to the weld after each weld impulse is applied to the weld to insure that the weld conforms to preselected standards.
It is still another object of the present invention to provide an improved welder control system as described which has the capability of applying corrective action to the weld as it is being applied to the work by shortening or lengthening either the cool or heat portion, or both, of the weld cycle to insure that the temperature of the weld follows certain preselected standards.
It is another object of the present invention to provide an improved resistance welder control system which is capable of indicating when corrective action is being taken and when the weld is such that corrective action cannot be taken.
It is a further object of the present invention to provide an improved bank peak detector circuit for use in conjunction with an impulse welder control system.
It is a further object of the present invention to provide an improved interface state control counter for use in conjunction with an improved welder control system.
It is still a further object of the present invention to provide an improved analog to digital conversion control and timing circuit for use in conjunction with an improved impulse welder control system.
It is still another object of the present invention to provide an improved data control circuit for use in conjunction with an improved welder control system.
It is still a further object of the present invention to provide an improved multiplexer control circuit for use in conjunction with an improved impulse welder control system.
It is still a further object of the present invention to provide an improved analog multiplexer circuit for use in conjunction with an improved impulse welder control system.
It is still another object of the present invention to provide an improved shift register and gating circuit for use in conjunction with an improved impulse welder control system.
It is another object of the present invention to provide an improved analog to digital circuit for use in conjunction with the impulse welder control system described above.
It is a further object of the present invention to provide an improved increment data and data ready circuit for use in conjunction with the improved welder control system described above.
It is a further object of the present invention to provide an improved start impulse interrupt circuit for use in conjunction with the improved impulse welder control system described above.
It is a further object of the present invention to provide an improved sample bank control circuit for use in conjunction with the improved impulse welder control system.
It is another object of the present invention to provide an improved end of weld interrupt circuit for use in conjunction with the invention.
It is a further object of the present invention to provide an improved thumb wheel circuit for use in conjunction with the welder control system described above.
It is another object of the present invention to provide an improved new wheel control circuit for use in conjunction with the welder system described.
It is still a further object of the present invention to provide an improved welder impulse control circuit.
It is still another object of the present invention to provide an improved device address decoding circuit for use in conjunction with the impulse welder described above.
It is still a further object of the present invention to provide an improved control system for sensing malfunctions and dead welds and an improved thermal printer circuit for use in conjunction with the impulse welding system described above.
It is still another object of the present invention to provide an improved light control circuit and tape reader circuit for use in conjunction with the system described above.
It is a further object of the present invention to provide an improved impulse welder control system which is inexpensive to manufacture, easily installed and reliable in operation.
It is a further object of the present invention to provide an improved welder control system for correcting standard weld procedures and which is capable of being interconnected with standard resistance welding control circuits.